[ovs-discuss] Open vSwitch with Xen Server?

Damiano Verzulli damiano at verzulli.it
Tue Jan 7 10:29:26 UTC 2020

On 06/01/20 22:16, Michael Cropper wrote:
> Hi, 
> I've been reading conflicting information on various websites about how
> to get the two working together. Some say that the Open vSwitch software
> should sit on the HostOS, others say it should sit on a GuestOS VM. My
> thoughts are that it should sit on a GuestOS VM - am I correct in
> thinking this?

as far as I remember, starting from versione 7.0 of XenServer, the default
"bridge engine" running on the "host" is OpenVSwitch (where, previously, it
was the standard "linux-bridge" one).

So, again, from version 7 onward, you have OpenVSwitch running on the host,
by detault.

I've been succesfull in leveraging such OVS toward a VM. In detail:

  * I've "manually" configured a GRE tunnel between the local instance of
    OVS (running on the XEN host) and a remote-host (a standard CentOS box,
    running a properly configured OVS instance);
  * on the Xen Host
      o such a GRE tunnel was "binded" to one of the default XenServer
        bridges (xenbr3), connecting the phisical nic (eth3) of the
        XenServer host;
      o a dedicated XenServer network was configured so to deliver it to
        VMs (aka: binded to xenbr3);
      o a VM (let's call it 'VM1') has been created and configured with a
        virtual interface connected to such a network

The all of the above was done in order for VM1 to access the remote network
(the one behind the remote GRE tunnel endpoint), at Layer2 (so to track
MAC-addresses of remote hosts).

It worked flewlessly, apart from some (planned and expected) MTU issues
(solved with IPtables forcing MSS on TCP connections)

In short: starting from XenServer 7, you can "play" with OVS both on the
host and on the guests.... assuming you are able to move yourself "safely"
inside such a relatively-complex scenario :-)



Damiano Verzulli
e-mail: damiano at verzulli.it
"Technical people tend to fall into two categories: Specialists 
and Generalists. The Specialist learns more and more about a 
narrower and narrower field, until he eventually, in the limit, 
knows everything about nothing. The Generalist learns less and 
less about a wider and wider field, until eventually he knows 
nothing about everything." - William Stucke - AfrISPA

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